external IP and port forwarding connection question

[ZeroX4]

can someone clear my mind about do i need hamachi or any other stuff like that if i have external IP or he could port forwarding and i want to play with my cousin:

1. when he would play on his pc and im on my pc PPSSPP to PPSSPP im host with external IP
2. when he is in my house he is on PSP im on PPSSPP (i have WiFi usb dongle)
3. when we are both on PPSSPP each on own pc but he is host port forwarding

also is it any difference if PPSSPP is host or PSP?

i dont need detailed answers i just need something like "yes" "no" "read tutorial"